The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as defined by the Jun. 20, 1990 Directive 09/385/CEE of the Council of the European Communities, as it relates to pacemakers, defibrillators and/or cardiovertors that are able to deliver low energy pulses to the heart for the treatment of heart rate disorders. This invention more particularly relates to prostheses known as xe2x80x9cmultisite devicesxe2x80x9d in which electrodes are respectively placed in distinct sites comprising at least one ventricular site and at least one atrial site. Examples of such multisite type prostheses include a xe2x80x9cdual chamberxe2x80x9d prosthesis, e.g., a pacemaker capable of right atrial stimulation and right ventricular stimulation, a xe2x80x9ctriple chamberxe2x80x9d prosthesis, e.g., right atrial stimulation and double (left and right) ventricular stimulation, and a xe2x80x9cquadruple chamberxe2x80x9d prosthesis, e.g., double atrial stimulation and double ventricular stimulation.
It has been proposed that, in addition to the treatment of heart rate disorders, myocardial contractions in patients suffering from cardiac insufficiency may be treated by stimulation. This is so whether the myocardial contraction disorders are spontaneous or induced by a traditional stimulation. The studies of J. C. Daubert et al., Stimucoeur, no. 3, pp. 170-176, which give a complete report on this subject, can serve as a point of reference in this matter.
It was, in particular, a proposal to switch to stimulating simultaneously the left and right ventricles for the resynchronization of cardiac activity which made it possible to observe frequently results that were quite spectacular for patients suffering from a Class III cardiac insufficiency, especially for those patients who did not benefit from more traditional treatments. The patient obtains an instantaneous benefit from such a treatment, resulting in the patient""s having a renewed gusto for life and, in certain cases, allowing the patient the possibility of partaking again in activities that were heretofore impossible. However, as the patient""s cardiovascular system is not rehabilitated as rapidly as the cardiac sufficiency can be improved, and does not have sufficient time to adjust to improved cardiac sufficiency, the resumption of an almost normal lifestyle by the patient can often place very taxing demands upon what is still a fatigued and ill heart.
However, in these circumstances, the physician neither can limit the capacity of effort of the patient (also called xe2x80x9ceffort capacityxe2x80x9d), i.e., restrict the amount of exertion undertaken by the patient for too lengthy a period, which would effectively reduce the effectiveness of the device, nor reexamine the patient at shorter intervals.
It is an object of the present invention to remedy the problems outlined above by providing the patient with a progressive effort capacity, which capacity evolves automatically over time.
Broadly, the present invention proposes to adapt a parameter known as xe2x80x9cmaximum frequencyxe2x80x9d or xe2x80x9cFmaxxe2x80x9d, which is the maximum follow-up frequency of the atrial rate by the ventricle, i.e., the higher limit to which a pacemaker can synchronize a ventricular stimulation on each atrial detection in a conventional DDD pacing mode. This parameter Fmax is used, in particular, to determine a maximum frequency limit for the stimulation frequency as calculated by a control algorithm, such as the algorithm that implements the functions of rate smoothing or rate control.
In a dual chamber pacemaker, the maximum frequency also serves as a reference value and is compared to the detected atrial frequency in order to limit the ventricular stimulation frequency when the atrial rate exceeds the maximum frequency value, for example, by applying an operating mode called the xe2x80x9cWenckebachxe2x80x9d mode. Heretofore, the maximum frequency has been more or less programmed permanently at a predetermined value, selected mainly according to the patient""s age, and eventually adjusted to take into account the patient""s effort and/or the presence of any cardiopathy or cardiomyopathy.
The invention thus also is directed to a device of the xe2x80x9cmultisitexe2x80x9d type comprising resynchronized cardiac stimulation for the treatment of cardiac insufficiency, characterized in that the invention includes gradually increasing, over a period of time, the maximum frequency of stimulation, from a starting or initial value up to a target value. Preferably, the maximum frequency is gradually increased by successive increments at regular intervals.
In one advantageous embodiment, when the device also comprises means for shortening the atrio-ventricular delay as the instantaneous heart rate increases, the device then also comprises means for comparing the instantaneous heart rate to a predetermined threshold, and means for allowing for the reduction of the atrio-ventricular delay to occur only when the instantaneous heart rate is above the threshold.
In an alternate embodiment, the invention may advantageously comprise means for lengthening the atrio-ventricular delay, which can be gradually lengthened as the instantaneous heart rate increases.
Optionally and advantageously, the value of the predetermined threshold can be gradually raised over time.